1. Field of the Invention
This invention relates to an ion beam generating apparatus, a film-forming apparatus, and a method for the formation of a film. More particularly, this invention relates to an ion beam generating apparatus suitable for production of a metal ion beam containing polyelectrolytically dissociated ions in a large proportion and having a large electric current, a film-forming apparatus and a method for the formation of a film, the both suitable for the formation of a film containing impurities only sparingly and excelling in quality.
2. Description of the Related Art
As techniques for producing a metal ion beam, methods which are depicted in FIG. 6 and FIG. 7 have been heretofore known. These methods operate with the procedure which comprises vaporizing a substance forming a cathode by virtue of vacuum arc discharge and ionizing the resultant vapor thereby forming a metal plasma and extracting a metal ion beam from the metal plasma (Japanese Unexamined Patent Publication No. 276,858/1988).
In an apparatus illustrated in FIG. 6, a cathode 2 formed of a work blank as an ion source is opposed to an anode 3 across an interposed space inside a vacuum chamber 1. The anode 3 is kept in place with a conically shaped retaining member 4 and is provided at the leading terminal thereof with an opening for release of ions. To generate an ion beam, first a feeble discharge is produced between the cathode 2 and a trigger electrode 5 disposed concentrically thereto and an arc discharge is consequently induced between the cathode 2 and the anode 3. The arc thus generated has intensity enough to vaporize part of the cathode 2 and form a plasma. The generated plasma moves in the direction of the anode 3 and passes through the opening of the anode 3. To control this movement of the plasma jet, a coil 6 disposed outside the vacuum chamber 1 forms a magnetic field. A set of ion extracting electrode 7 is disposed at a stated distance from the anode 3. By this ion extracting electrode 7, ions are extracted from the plasma which has passed the anode 3.
In an apparatus illustrated in FIG. 7, a rotatable holder 9 is disposed inside a vacuum chamber 8, a plurality of cathodes 10 are retained at equal radial positions on the holder 9, and an anode mask plate 12 for retaining an anode 11 is fixed in front of the holder 9 as opposed to the cathodes 10. Further, an ion path 13 is formed on a line parallel to the axis of rotation of the holder 9 on the radiuses including the positions of the cathodes 10 in the vacuum chamber 8. An ion extracting electrode 14 is disposed in the ion path 13. Inside the vacuum chamber 8 behind the ion path 13, a trigger electrode 15 is set in close proximity to the cathode 10.
In this apparatus, the cathodes 10 are disposed at suitable positions in the ion path 13 so as to allow formation of an arc plasma relative to the different cathodes 10.
In the conventional ion beam generating apparatuses of this class, an ion beam is directly extracted from a metal plasma which is formed by vacuum arc discharge. As a result, these apparatuses have the disadvantage that the proportion of polyelectrolytically dissociated ions in the ion beam is very small and the ion extraction system for imparting a prescribed energy to the ion beam must be given a large power supply capacity.
A film-forming apparatus constructed as illustrated in FIG. 8 to accomplish the formation of a film by the use of a metal plasma generated by vacuum arc discharge as described above has also been known. In the film-forming apparatus illustrated in FIG. 8, a cathode 17 and an anode 18 provided with an opening part are opposed to each other across an intervening space inside a vacuum chamber 16. The cathode 17 is provided on the anode 18 side thereof with a mechanically operably constructed trigger electrode 19. On the lateral side of the anode 18 is disposed a holder 21 for retaining a substrate 20 intended to allow formation of a film thereon.
In this film-forming apparatus, vacuum arc discharge is initiated by an arc power source 22 applying voltage and the trigger electrode 19 meanwhile beating the cathode 17 and the vacuum arc discharge is generated between the cathode 17 and the anode 18 and an arc plasma is consequently formed. Then, a film is formed by causing ions in the arc plasma to be deposited by means of a bias power source 23 on the substrate 20 which is set at a prescribed potential.
The conventional film-forming apparatus of this class, however, has the disadvantage that impurities originating in the trigger electrode 19 and the anode 18 mingle with the formed film and impair the quality of the film. When the apparatus uses a mechanical trigger mechanism, it entails an operational problem.